Just my humble 2 cents. I too have a 2007 Elise since new, with Rotrex supercharger a very sporty little car. And I had a P4SS from 2012 to 2015, converted to LHD especially for me. It was my most exciting Morgan, the pinnacle of racing cars with good road capability. Because it would never have passed the MOT legally (no OBD2) I sold it with a heavy heart after 3 years to someone who only drives it on the track.
If I were you, Ted's owner, and this is my completely subjective opinion that should not offend anyone else, I only know SSL as a passenger, it was very comfortable. It would not suit a P4SS as well, it is no longer the authentic quaint Morgan it should be. SSL is comfort but on a P4SS it's like a fabric softener.
I would watch for another issue, 2011 was a year of the worst leaf springs at MMC. My new P4SS completely sagged in the rear on the driver side after only three quarters of a year. I got new leaf springs under warranty that held up well until I sold it. Ask if yours are still original, if they perform you don't have to change but most likely you have to.
If I were that new to everything Morgan I wouldn't directly replace an 80 year old design without even getting to know it. For me the leaf spring belongs to the traditional Morgan like the hydro-pneumatics to the old Citroen. If you want to drive very comfortably, you have other cars for that and the Morgan remains intense and unfiltered in the experience. But as I said, that's just me, you or others may like SSL well in the P4SS.
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